1. Field of the Invention
The present invention relates to a system for supplying a lubricant to an equipment article, and more particularly to a selectively operable system for replenishing an equipment article with a supply of lubricant.
2. Description of Background
Systems are known for supplying a lubricant to a wheel bearing assembly or another equipment article. Prior art systems of a well known design maintain a constant level of lubricant in an article of equipment by providing a spring-loaded or other pressure-responsive components that constantly force lubricant into the equipment article.
U.S. Pat. No. 5,303,800 issued to Persson describes a system including a lubricant-holding reservoir attached to a wheel hub. The reservoir is in fluid communication with the hub, and includes a bellows that is responsive to pressure changes within the hub. The bellows serves as a movable wall for containing lubricant within the reservoir. Pressure-responsive movement of the bellows maintains a constant lubricant level in the wheel hub.
Several references, including U.S. Pat. No. 4,941,595 issued to Blake, U.S. Pat. No. 4,106,816 issued to Prokop, and U.S. Pat. No. 4,106,816 issued to August describe lubricant-supplying systems including a grease chamber disposed within a cylindrical housing, a spring-loaded plate slidably mounted in the housing, and a grease fitting provided in the housing for charging the housing with grease and forcing the spring-loaded plate outwardly. The spring-loaded plate continually exerts pressure against the grease and causes the grease to enter the wheel bearing housing and coat the wheel bearings.
Pressure-responsive systems of the type described above exhibit various disadvantages and limitations. Systems of the type described are designed to constantly supply lubricant to an equipment article requiring lubrication and are not easily adapted for selective release of lubricant into an equipment article. If systems of this type are modified for selective replenishing, then the mass of lubricant released is not easily controlled. Further, the rate of lubricant flow in these systems is not easily controlled. Still further, many of these systems require rather sophisticated mechanical components which are susceptible to breakdown.
Lubricant replenishing systems are often implemented in spacecraft applications. Bearing lifetime in a spacecraft spin bearing is limited by the lubricant supply. The bearings operate under very little stress, and as long as lubricant is present, their lifetimes are essentially infinite. The initial charge of lubricant will eventually be depleted due to evaporation in vacuum, and surface migration. It is presently accepted that a grease lubrication system will provide ample lubricant to a spin bearing system for a minimum of 8 years. If the lubricant were replenished during the mission, the lifetime of the mechanism could theoretically be doubled, extending the mission life to 16 years.
On-orbit relubrication of space flight mechanisms has been a long-standing problem. Others have solved the problem, but either in a complex manner resulting in questionable reliability or at a high cost. The existing solutions are generally limited to the replenishment of oil, whereas a grease replenishment system would be preferred.
There exists a need for a low cost lubricant replenishing system which can be adapted to selectively and remotely replenish an equipment article with a supply of a lubricant, and which releases lubricant into the equipment article at a rate that is easily controlled.